Rotary encoders are used to measure rotary motions of a rotationally mounted body, particularly a shaft, over one or more rotations. In so doing, the rotary motion is recorded incrementally or absolutely. In connection with gear racks and gear wheels or with threaded spindles, linear motions can also be measured by a rotary encoder.
Rotary encoders are used in large numbers as what are termed motor-feedback devices, and in this practical application, are used to form position or angle information, which is utilized for the commutation of electrical drives. For example, in the case of synchronous motors, information about the absolute rotor position is needed immediately after the supply voltage is switched on. Rotary encoders with additional commutation signals—they supply relatively rough position information—and absolute rotary encoders in singleturn or multiturn design, which output the exact angular position immediately with a few angular seconds accuracy, are suitable for this purpose.
During the mounting of these measuring devices, the rotor positions of the electric motor and of the rotary encoder must be assigned to each other in order to achieve the most constant motor currents possible. An inadequate allocation with respect to the electromotive force causes considerable motor noise and high power losses.
In the case of conventional rotary encoders, for this purpose, initially the rotor of the electric motor, i.e., its shaft, is brought into a preferred position by applying a direct current. Rotary encoders with commutation signals are then roughly aligned, e.g., with the aid of marking lines on the rotary encoder or a reference-mark signal. The shaft of the rotary encoder is then mounted on the shaft of the electric motor. The precision adjustment is then made with the aid of a phase-angle measuring device, in the course of which, the stator of the rotary encoder is rotated until the phase-angle measuring device indicates approximately the value zero as distance to a reference mark. Finally, in this position, a compensating coupling, particularly a stator coupling, can be fixed in position on the motor housing.
Absolute rotary encoders are first completely mounted. Thereupon, the value “zero” is assigned to the preferred position of the electric motor by a zero shift. Electronic equipment, including an appropriate software package, e.g., in a computer connected to the rotary encoder, is used as an aid for this purpose. A zero shift is thereby able to be performed.
German Patent No. 197 29 452 describes an adapter component which permits an angle-wise allocation between a rotary-encoder shaft and a motor shaft. The stator must be rotated for the precision adjustment here, as well, and finally a stator coupling must be affixed to the motor housing.
Conventional devices having stator couplings have the disadvantage that the precision adjustment must be carried out in the field individually for each installation situation, and that frequently a fixation of the mechanically sensitive compensating couplings is then necessary in the field.
It is also conventional that the attachment of rotary encoders which supply commutation signals may be simplified by mechanically coded rotor couplings, as described, for example, in PCT International Published Patent Application No. WO 2008/034768. However, a use of rotor couplings is always accompanied by losses in the accuracy of the commutation signals.